HEAT-TRANSFER CHARACTERISTICS IN LOW-TEMPERATURE LATENT-HEAT STORAGE-SYSTEMS USING SALT HYDRATES

Heat transfer characteristics of a low temperature latent heat storage system have been determined for the circular finned and unfinned tubes using sodium acetate trihydrate as a phase change material (PCM). In the heat storage stage (melting process), the PCM heat transfer coefficient in the unfinned-tube system showed good agreement with the calculated value by the heat conduction equation. The heat transfer between the tube wall and the PCM was not enhanced by the fins in the thin-finned-tube system, whereas 2 times higher heat-transfer coefficient for the thick-finned-tube system over the unfinned-tube system was obtained. The experimentally determined heat-transfer coefficients in the unfinned-tube and thick-finned-tube systems are in the ranges of 40-170 and 80-320 W/m(2)-k, respectively. The amount of heat storage for three systems has been correlated in terms of Fourier, Stefan and Reynolds numbers. The thermal performance of heat storage systems are found to be strongly dependent on the inlet temperature of heat transfer fluid.